The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Mobile devices have to be charged repeatedly in order to be used. To avoid tediously connecting a charger by plug and socket to do this, systems for wirelessly transferring power are increasingly being used. The alternating inductance between two magnetic coils is utilized here to transfer electrical output through magnetic induction. A distinction is generally made between inductive and resonant systems, with hybrid forms also being available. In an inductive system, a source coil acting as the primary winding of a transformer is fed by a voltage source or a current source. A receiving coil acting as a secondary winding of a transformer is connected directly or through a resonant coupling capacitor to a bridge rectifier. In a resonant system, the source and receiving coils are coupled to capacitors to form electrical oscillating circuits, so that a portion of the reactive impedance of the coils is canceled. This ultimately results in such systems being optimized onto a narrow frequency band in which the electric power is transferred.
Since the charger and the mobile device to be charged must be tuned to one another, various standards have established themselves in the field of the wireless transfer of power. The Qi standard issued by the Wireless Power Consortium (WPC) is usually classified as an inductive charging standard. Although a resonant capacitor is used in reference circuits, the quality factor Q lies in the single-digit range; this implies that no resonance is effectively used. The electrical power here is transferred in a frequency range of 88 Hz-205 Hz. In the automotive environment, it is not beneficial to actuate the output stage before the transfer coil by means of a square-wave signal, as this leads to a high electromagnetic radiation/noise emissions and/or electromagnetic incompatibility. Especially in the vicinity of sensitive vehicle modules such as radio, ABS, and automatic pilot, this situation can only be alleviated with expensive shielding measures in the vehicle and surrounding the charger.
Chargers for inductively charging battery-operated mobile devices inside a motor vehicle are described, for example, in US 2016/0301236 A1, US 2014/0239732 A1 or WO 2015/177657 A1.